Elongated manifold blocks typically have a central inlet passage that delivers hot melt from an extruder or other source into the center of the block and then splits it into a main runner that delivers the melt to a series of injection nozzles spaced along the length of the manifold body. While various means are typically utilized to keep the body hot so that the melt flows properly at all times, the opposite ends of the manifold are typically exposed to ambient air. Consequently, passages associated with the endmost nozzles are difficult to maintain at the same high temperatures as other passages in the body. Moreover, structures utilized to support the manifold often function as heat sinks to draw off disproportionate amounts of heat in end portions of the body and compound the problem.
The present invention addresses this problem by providing a way of supplying auxiliary heat specifically to opposite end portions of the manifold body in addition to that which is supplied to the body as a whole. Furthermore, the temperature in at least one of the end portions is sensed separately from the rest of the body to control the auxiliary supply of heat separately from the main supply, with a view to establishing a uniform temperature throughout the entire body if at all possible.
In a preferred form of the invention, each auxiliary source of heat is a generally flat electrical resistance type heater applied to each end surface of the manifold body. Preferably, the heater covers the entire exposed surface of the end of the body. In addition, in order to reduce the amount of heat drawn off by supports at the corners of the body, a pair of isolating slots extend transversely through the entire body and are located generally between each support and the melt passages in the upper and inboard regions of the body. In a preferred form, each isolating slot is generally L-shaped, having a vertical leg that is shorter than the horizontal leg and with the horizontal leg extending inwardly toward the center of the body from the bottom of the vertical leg.